thats weird.. my old friend from college had peroxide blonde hair, and she put blue through her fringe one day and it took really well, but she had to re-do it every week or so =/
It's a poor sticker for sure. Blues and greens never fade too elegantly either...they go to a weird greyish tone quite soon. I've been able to let my pink dyes fade all the way back to blonde, and they never look awful, just an increasingly pale pink. Well maybe have a go at mixing with a spot of warm dye, see if that does anything.
Love that shade of purple on you two. (you two are beautiful!) I've dyed myhair purple once and it faded it a pink/brown, and once a deep blue which faded horrible to swamp green.
i had pink bits in my hair once, they faded to a nice shade of ginger then ive had green and that went kinda funky yellow! i think red fades best